Abstract: In the PASER (particle acceleration by stimulated emission of radiation), the energy stored in an active medium transferred directly to the electron beam passing through in discrete amounts by emitting a photon when the bounded electron returns from upper to lower energy state. In this paper, the wake-field generated by a bunch of electrons traversing in an active medium has been discussed. The calculations of the development of amplitude for gas mixture active medium about and ArF were made respectively. The results show that the gradient can reach around 1GeV/m，which is about two orders of magnitude larger than that in normal acceleration structure (such as disk-loaded waveguide acceleration structure) in present . In addition, the electron energy gain occurring as a train of electron micro-bunches traversing in gas mixture was analyzed by a two dimension model. The train of micro-bunches can obviously gain energy from the active medium and the energy exchange is linearly proportional to the interaction length d. The influence of the bunch figure and other quantities on the energy exchange occurring as a train of electron micro-bunches traversing gas mixture were investigated when the interaction length is 0.5m. The results illustrate that maximum electron energy gain can be obtained by the train of micro-bunches with optimized parameters.

Key words: PASER, active gas mixture, accelerating gradient, energy gain